Radio receiving system



Aug. 13, 1929. A. E. HARPER RADIO RECEIVING SYSTEM Filed Aug. 2e, 1925 Patented ug. 13, 1929.

UNITED STATES PATE 'I' FFCE.

AUGUSTUS E. HARPER, OF BELFAST, MAINE, ASSIGNOR T AMERICAN TELEPHONE AND 'IELEGRAPI-I COMPANY, A CORPORATION 0F NEW YORK.

RADIO RECEIVING SYSTEM.

Application filed August 26, 1925.

This invention relates to radio receiving systems and particularly to means for im proving the directional selectivity of such systems.

Various ways for improving the directional selectivity of radio signaling systems have been proposed and used heretofore. .Certain of these employ a plurality of vertical antennae spaced apart a definite fraction of a wave length so that the voltages resulting from received signaling waves will have such phase relationship as to combine if thesignal is from the desired direction or to be opposed and neutralized if the signaling wave i setting up the voltage is from an undesired direction. Other forms of directional selecting systems employ a wave antenna or a plurality of such antennae arranged parallel geographically which have a receiving char-` acteristic highly receptive in a certain direction and diminishing in receptivity in other directions.

In the copending application of H. T. Friis, Serial No. 746,753 filed October 1924:, is described a radio receiving system employing two loops spaced apart a` definite fraction of a wave length and so connected with circuits adapted to control the phase of the resulting potentials as to have a reception characteristic similar to that of a wave antenna. An arrangement7 such as disclosed in the Friis application, has decided advantages over the system employing a wave antenna or a system employing an antenna array in view of the fact that the physical dimensions of the antennae employed are so much smaller in the Friis system than in any other known system. rIhe Friis receiving system is also fully described in a paper published in the Proceedings of the Institute of Radio Engineers, vol. 13, page v685, et seq. This paper was p resented to the institute on May 6, 1925.

The object of this invention is to obtain greater selectivity than that produced by the arrangement shown in the said Friis application, the improvement being effected by an arrangement capable of increasing the intensity of the voltage set up in the system by waves from the desired stations and diminishing in intensity waves from undesired sources or stations.

The invention will be clearlyunderstood from the following description when read in connection with the attached drawing lin Serial No. 52,642.

which Fi re 1 shows schematically one form of t e invention; and Figs. 2 and 3 illustrate the principle upon which the invention rests.

In Fig. l are shown two complete receiving systems designated A and B, each of which is substantially like the other and both of which are connected to a common receiving circuit for the reception of signals. The receiving system A comprises two loops A, and A2, each represented by an induct-ance and a variable capacity by means of which the loops may be tuned to the frequency desired to be received. The loops are arranged so that they will lie in substantially the same plane which is perpendicular both to the ground and to the wave front of the desired wave. The loops of both receiving systems, as indicated in Fig. 2, are oriented about a common axis. The loop A1 is 75 connected with the input side of the signal frequency detector tube D1 and similarly the loop A2 is connected with the tube D2. The input circuit of the tube D1 includes a winding 1, which is coupled with the windings of the variometer 2 by means of which oscilla- 2 tions of the beating frequency are supplied by a source O common toV receiving systems A and B for the purpose of bea-ting the incoming frequency to an intermediate Afrequency, the purpose of which will be clear from subsequent description. In similar manner, the input circuit of the tube D2 includes a winding 3 which is coupled with the winding 4 of a circuit connected with the said source of beating oscillations. The winding 3 is adapted to be connected in one direction with the input circuit when the arms of the switch 5 are thrown upwardly and in the opposite direction when the said arms are thrown downwardly. The object of the reversing switch is to control the phase of the voltage from the beating oscillator applied to the tube D2 in order to effect thevproper combination of this voltage with the voltage resulting from the loop A1. The output circuits of the tubes D1 and D2 are joined and connected with the input side of an intermediate frequency amplifier 6, the output side vof which is connected to an intermediate frequency detector 21 which, in turn, is connected with the signal receiving apparatus 22. The common circuit from the tubes D1 and D2 includes a winding 7 which is coupled with the coils of the variometer 8 connected with the detectors D3A yand Det of system B, for the purpose of controlling the phase of the intermediate frequency currents applied to the said amplifier by .the severa-l groups of detectors. This common circuit also includes an intermediate frequency filter 9 which is adapted to control the range of the frequencies applied to the intermediate frequency amplifier and detector. The beating. oscillatorO, which includes the oscillating tube 10 and the usual feed-back circuit, is connected with the input side of the amplifier 11, the output circuit of which is connected with a phase control circuit associated with and connected with each of the receiving' systems A and B. rl`hus, the output circuit of the amplifier 11 is connected by the conductor 12 with a phase control circuit forming part of the receiving system A,

comprising the inductance 4 and variable capacity 13 and also the variometer 2, the 1nductances 14 and capacity 15. The high frequency beating oscillations as amplified by 11 will flow over conduct-or 12 to ground at 16, part of the current flowing through the circuit including the condenser 13 and the inductance 4, and the remainder of the current flowing through the windings of the variometer 2 and through the condenser 15 and one ofthe inductances 14 to ground. By virtue of the coupling between the inductanc'e 4 and the inductance 3 on one hand and the windings of the variometer 2 and the inductance 1 on the other hand, a potential willbe applied to the input circuits of thel tubes D2 and D1 respectively which will beat the oscillations of the frequency received by the loops A2 and Al respectively to the same intermediate frequency and the -phase relationship of these intermediate frequency currents resulting fromr the beatingr operationwill be controlled by the phase control circuit. In likermanner the oscillations'received by the loops Bl and B2 of the receiving system B will'be beaten to an interphase control circuit similar to that de-` yscribed in connection with station A. Since the source of beating oscillations is the saine for both stations, the resultant intermediate frequency of the detector tubes D3 and D4 will be the same. This intermediate frequency current from station B will be transf mitted over conductor 17 to a phase control` circuitincluding the variometer 8, the variable condenser 18, the inductances 19 and the variable condenser 20. The intermediate frequency current from the station B will be controlled as to phase by the intermediate frequency phase control circuit which has just beentraced and as thus controlled will be impressed upon the winding 7 of the circuit connected withthe intermediate frequency amplifier 6 and the intermediate frequency detector. t will accordingly be seen, therefore, that after the high frequency currents received by each receiving system A and B have been reduced to currents of intermediate frequencies, these intermdiate frequency currents are combined under a definite phase condition and are amplified and detected. The distance between the two receiving systems A and B is approximately one wave length or a fraction thereof in a direction perpendicular to the direction of propagation of waves from a desired station.

The manner in which the system shown in Fig. 1 opera-tes will perhaps be more clearly understood if the mode of operation of a single receiving systemis irst described. As set forth in the'said copending' application of Friis, hereinbefore referred to, the voltage set up in the vloop A1 by a wave advancing in the direction represented by the arrow 1s e1=Ecos 0 cos wt (l) l and the voltage set up in the loop A2, which is separated from A1 by the distance a meters, is

e1+e2= E cos @init-l- Ecos 0 cos (wt- C%Q27r-b the maximum value of this voltage is v, That is to say, the loops Al and A2 are oriduced.A When this result obtains the switch 5 is thrown downwardly so that they winding 3 is connected into the circuit in the opposite y direction. The resultant intermediate frequency currents will be added instead of subrality of `receiving stations based upon thef Friis principle, having their intermediate frequency circuits connected and the phase relationship of those currents adjusted the resultant current will be much greater in the reception of signals from a desired station than in the Friis system. This will be evident from the following description when read in connection with Fig. 2 of the drawing. The voltage in each Friis receiving circuit will be V=4E1r cos 0 (l -cos 6) cos g1r sin @-1,0

where d is the distance between the systems and lp is a phase angle which may be adjusted to obtain certain desired results.

An example of an application of this system is given below.

Assume d 1r l 2:.- =90 i 2 t 0 Then 4l cos 9 (90) cos (90 0 cos 9 l-eos 6 2 0050) sm 9 sin 0 sin a) V Fig. 3 shows graphically these results when plotted to polar? coordinates. It will be seen that the directional selectivity in the above mentioned case, or ratio of front to rear receptivity is It will be apparent, therefore, that by means of my invention the selectivity of a receiving -system employing a plurality of spaced loop antennae is greatly increased along the lines of desired reception and greatly diminished in other directions.

lVhile the invention has been disclosed as embodied in a particular form it is to be understood that this is purely schematic since it is capable of embodiment in different forms without departing from the spirit and scope of the appended claims.

Vhat is claimed is:

l. In a directionally selective radio system, the combination with a receiving circuit comprising t-wo antenna both lying in the same plane and tiXedly held at a predetermined distance apart, the said plane being perpendicular to the ground and to the wave front, a detector individual to and connected with each antenna, a source of beating oscillations connected with the input side of each detector to produce an intermediate frequency from the received signaling frequency, the connect-ion including means to change the phase of the -said oscillations, a common output circuit for both detectors, of a second receiving circuit substantially similar structurally to said first receiving circuit and connected with the same source of beating oscillations, and an intermediate frequency detector and receiver connected with the output circuits of said first and said second receiving circuits, the connection including means to control the relative phase of the intermediate frequency currents applied to the said intermediate frequency detector.

2. In a directionally selective radio system, the combination with a receiving system comprising two loop antennae, means to support the said antennae in the same vertical plane and at a predetermined distance apart, the said plane being perpendicular to the ground, a plurality of demodulators each individual to and having its input circuit connected with an antenna, the output circuits of said demodulators being connected with a common output circuit, a source of beating oscillations connected with the input circuits of said demodulators to beat the incoming signal frequency to an intermediate frequency, one of said connections including a reversing switch to change the phase of the beating oscillations in said input circuit, a second receiving system substantially similar to the said first receiving system having similar antennae similarly supported, the antennae of both systems being oriented about a common axis parallel to the plane of the antennae and connected with the same source of beating oscillation-s, means connected with the second system to combine the intermediate frequency voltages of the first receiving system With those of the second receiving system and to control the phase of said voltages,'and an intermediate frequency detector and an indicating device Ato detect the signal from said combined voltages..

3. ln a system as set forth in claim 2, the method for effecting the reception of signals Which consists in'receiving Waves of signal frequency in the antennae of each receiving syst-em, beating the signal frequencyV With oscillations of a frequency differing from the signal frequency to produce the same intermediate frequency in all of the receiving systems, opposing in each system the intermediate frequency potentials so that they Will tend to neutralize and orientating the antenna; of both receiving systems about a common anis until full neutralization is effected, then changing the phase of the beating oscillaticns so that the said intermediate frequency potentials in each system will be in such phase relation as to produce an additive effect, combining ,the said intermediate frequency from both systems and detecting the signal from said intermediate frequencies.

4f. In a directionally selective radio system, the combination With a receiving circuit comprising two antennae both lying in the same plane and fiXcdly held at a predetermined distance apart, the said plane being perpendicular to the ground and to the Wave front, a detector individual to and connected i with each antenna, a source of beating oscillations connected with the input side of each detector to produce an intermediate frequency from the received signaling frequency, the connection including means to change the phase of the said oscillations, a common output circuit for both detectors, of a second receiving circuit substantially similar structurally to the said first receiving circuit and connected with the same source of beating oscillations, and an'intermediate frequency detector having its input side connested with the output circuits of the said first and said second receiving circuits.

5. In a dircctionally selective vradio system, the combination With a receiving circuit comprising two antennae both klying in the same plane and fiXedly held at a predetermined distance apart, the said plane being perpendicular to the ground andrto the Wave front, a detector individual to and connected with each antenna, a source of beating oscillations connected with the input side of each detector to produce an intermediate frequency from the received signaling frequency, the connection including ymeans to change the phase of the said oscillations, a common output circuit for both detectors, of a second receiving circuit substantially siniilar structurally to the said first receiving circuit and connected With the same source of bea-ting oscillations, and an intermediate frequency detector having its input side connected With the output circuits of the said first and said second receiving circuits, the input connection including means to control the relative phase of the intermediate frequency currents applied tothe input of the said intermediate frequency detector.

6. ln a directionally selective radio system, the combination With a receiving circuit coinprising two antennae both lying in the same plane and iiXedly held at a predetermined distance apart, the said plane being perpendicular to the ground anelito the Wave front, a detector individual to and connected with each antenna, a source of beating oscillations connected With the input side of each detect-or to produce an intermediate frequency from the received signaling frequency, the connection including means t0 change the phase of the said oscillations, a common output circuit for both detectors, of

a second receiving circuit substantially sim-v ilar structurally to the said first receiving circuit and connected With the same source of beating oscillations, and an intermediate frequency detector having its input side connected With the -output circuits of the said first and said second receiving circuits, the said input connections including a frequency selecting device capable of passing the intermediate frequency and a phase controlling vdevice to adjust the phase relation of the in-k termediate frequency currents applied by said output circuits to the input side of ther said intermediate frequency detector.

in" testimony whereof, 'I have signed my name to this specification'thisl24th[day of August 1925. y Y Y Y p Aneusfrus n HAR-Pen. 

